I wrote my preliminary questions and concern on Pfizer's vaccine here (or 5 posts below).
Moderna's clinical trial can be found here.
Essentially, I have the same questions/concerns for Moderna as I have for Pfizer (see that post), other than those questions Moderna already answered for us, that Pfizer hasn't yet (but I'm sure they will).
Otherwise, just a brief comparison of what I noticed is is similar and what is different, based on just a quick glance of both clinical trials from clinicaltrials.gov and press releases:
1. Both use the mRNA (or messenger RNA) of SARS-CoV2 rather than the actual virus.
2. Both were open-label trials, tested in phase 1 in healthy adults, with an extensive exclusion list; however, Moderna allowed some other health conditions within specific parameters, in phase 1 (see below). It is presumed both expanded their inclusion in phase 2 (results not yet published).
3. Both require cold storage (with Pfizer's cold storage requiring an unusual amount of cold - see below).
Again, off the cuff in a brief glance - what's different:
1. Pfizer's phase 1 trial was ages 12 and up, while Moderna's phase 1 trial was ages 18 and up.
2. Pfizer's phase 1 trial contained 43,000 participants, while Moderna's trial population contained 30,000 participants.
3. Though Pfizer's phase 1 trial was larger by 13,000, Moderna's was more inclusive (see below) and more effective - Pfizer's press release from phase 2 trials say it's 90% effective, Moderna's press release says 95% effective.
4. Pfizer ruled out essentially anyone with any other health condition for phase 1, while Moderna's phase 1 trial allowed certain health conditions within specific parameters - i.e. renal disease with an eGFR of <60, COPD requiring medications, severe heart disease requiring medications or intervention - which essentially means if you have these diseases, but do not yet require intervention, you could be part of Moderna's phase 1 trial. Also, you could be a recent smoker for Moderna's phase 1, but under 56 years of age.
5. Moderna's trial had an extremely careful focus on effects on reproductivity in both men and women, heavy emphasis on ruling out pregnant women - which is actually very, very wise, considering we don't know the effects of RNA therapies on reproduction yet. The reason for this is not because we have any evidence whatsoever that mRNA affects reproductivity, it's just that they're choosing to be safe rather than sorry - very smart.
6. Pfizer did not press release any information at all about the 10% of patients who failed the trial and contracted COVID anyway. Moderna claims the less than 5% who contracted COVID contracted the mild form.
7. Side effects for Pfizer's vaccine are preliminarily reported to be fairly significant - fevers, fatigue, aches from 2 days to a week, whereas Moderna claims less severe side effects that last a single day.
8. Pfizer's vaccine requires storage at -70 degrees Celsius, while Moderna's vaccine requires -20 degrees Celsius. This many not seem like a big deal to you and me at first, but it's a big deal for storage in pharmacies and healthcare facilities that are not equipped with cold-storage facilities to that degree - which means we will care, because this will incur an extra expense that will be tacked on to insurance bills.
I'm still concerned about the safety and tolerability of both, especially long term, and still have more questions - as I said, for those, see the post on Pfizer.
It will also depend on what my insurance company allows (which essentially will boil down to contracting and who offers them the best contracts/rebates, unfortunately), and I would have to do more research, but if these were the only two options over time, I'm leaning towards Moderna - IF I eventually feel the vaccine is safe over time.
The reasons for this are not just better overall efficacy, but because Moderna had a more inclusive phase 1 trial from the get-go, still within specific parameters, but still turned out with better efficacy; they were extremely careful when it came to concerns about monitoring for any mRNA effects on reproductivity in both men and women, and were very specific in what type of COVID phenotype the participants who failed the trial contracted.
Above all, I admit, I may have a bias because Moderna isn't "Big Pharma" - they're a smaller company, which means they aren't privy to political investment and influence - at least not yet ;)
But again, same concerns/questions I had for Pfizer's vaccine still apply, before I do.